The present invention relates to a paper stacking apparatus for a sheet-fed press, which stacks, on the paper stack plate of a paper feed apparatus, paper sheets to be supplied to a printing unit.
FIG. 3 shows a paper stacking apparatus of this type proposed by the present applicant and disclosed in Japanese Utility Model Laid-Open No. 1-109020, in which the front portion of the paper stacking apparatus in the feed direction to a printing unit is the left side of the drawing. Referring to FIG. 3, a pair of left and right elevating bars 3 are respectively hung by elevating chains 2 from a pair of left and right paper feed frames 1 each formed in an inverted L-shape when viewed from the side surface. When the elevating chains 2 are wound up or rewound by driving units (neither are shown) to cause projections 6 to engage with grooves 4a of guide support columns 4, respectively, and at the same time, rollers 9 supported on the elevating bars 3 through brackets 7 and arms 8 are respectively engaged with grooves 5a of guide support columns 5 to vertically move the elevating bars 3.
Each roller 9 is biased by a compression coil spring 11 interposed between the swingable arm 8 and a spring seat 10 standing on each elevating bar 3 in a direction to be pressed against the corresponding groove 5a. More specifically, when the roller 9 is pressed against the groove 5a by the biasing force of the compression coil spring 11, the elevating bar 3 is biased forward, i.e., to the guide support column 4 side by the reactive force.
On the other hand, cams 12 each having an inclined surface 12a are fixed on the base end faces of the frames 1 close to the left and right elevating bars 3. Rollers 13 pivotally mounted on the elevating bars 3 are pressed against the inclined surfaces 12a by the biasing forces of the compression coil springs 11, respectively.
A pair of bars 14 are integrally supported on the front and rear portions of each of the left and right elevating bars 3. A rectangular paper stack plate 16 on which paper sheets 15 are stacked is mounted on the pair of bars 14. A plurality of vertical front gauges 17 are disposed in front of the paper stack plate 16. The paper sheets 15 are stacked while the leading ends thereof are kept in contact with the front gauges 17, thereby aligning the leading and trailing ends of the paper sheets 15.
With the above arrangement, when the elevating chains 2 are rewound to cause the elevating bars 3 to move downward to the lower limit before the printing operation, the rollers 13 are moved from the lower portions of the inclined surfaces 12a to the higher portions. The elevating bars 3 are thus moved backward, i.e., toward the guide support columns 5 sides against the biasing forces of the compression coil springs 11.
After stacking the paper sheets 15 on the paper stack plate 16 outside the machine frame, the paper stack plate 16 is conveyed onto the bars 14 integral with the elevating bars 3 by a handlift or the like. At this time, the leading ends of the paper sheets 15 are brought into contact with the front gauges 17 and aligned. Since the elevating bars 3 are pressed by the cams 12, and the rollers 9 are pressed against the grooves 5a while compressing the compression coil springs 11, the elevating bars 3 are stable to prevent the paper sheets from fluttering.
When the printing operation is started after stacking the paper sheets 15, the paper sheets 15 are drawn one by one by a sucker apparatus (not shown) and supplied to the printing unit, thereby performing printing. In accordance with paper feeding, the elevating chains 2 are intermittently wound up to cause the elevating bars 3 to move upward. At this time, the roller 13 are released from the pressures at the higher portions of the inclined surfaces 12a of the cams 12. The elevating bars 3 are moved forward by the biasing forces of the compression coil springs 11.
The leading ends of the paper sheets 15 integral with the elevating bars 3 through the paper stack plate 16 are pressed against the front gauges 17 and aligned. Even after the elevating bars 3 are moved further upward to keep the rollers 13 away from the cams 12, the paper sheets 15 are pressed against the front gauges 17 by the biasing forces of the compression coil springs 11, and movements in the left and right directions are regulated by the guide support columns 4 and 5. Therefore, the paper sheets 15 do not flutter even when they are hung by the elevating chains 2.
As described above, in the conventional paper stacking apparatus, the paper sheets 15 stacked on the paper stack plate 16 are stable. However, when the paper stack plate 16 on which the paper sheets 16 are stacked is conveyed onto the bars 14 by a forklift or the like, if the left and right sides of the paper sheets 15 stacked on the paper stack table outside the machine frame are not aligned and the paper sheets 15 are skewed, the entire paper sheets 15 are not uniformly brought into contact with the front gauges 17, and sometimes, some of the paper sheets 17 are not in contact with the front gauges 17. If the printing operation is started in this situation, the paper sheets 15 clog during conveyance to cause an increase in waste paper, or a printing trouble is caused to degrade the quality of printed matter. In addition, since much time is required to correct the skew of the paper sheets 15, the preparation time is prolonged to degrade the operating ratio of the printing press.